Method of generating electricity and electrical generator

ABSTRACT

An electric generator for deriving electrical energy from oscillatory motion such as that of buoys, vehicles and animals. The generator has a stator and an armature coupled together by spring means and effective to generate current when bodily movement of the generator causes, by inertia effects, relative movement of the armature and stator. Particular application is in powering oceanographic buoys.

United States Patent Last et al.

[54] METHOD OF GENERATING ELECTRICITY AND ELECTRICAL GENERATORinventors: James David Last, Llanfairfechan;

David N. E. Rowe, Great Baddow,

both of England Bangor, North Wales Filed: June 30, 1970 App]. No.:51,281

Foreign Application Priority Data June 30, 1969 [56] References CitedUNITED STATES PATENTS Assignee; University College of North Wales,

Great Britain 33019169 US. Cl ..290/53, 310/15 Int. Cl ..F03b 13/12Field of Search .....290/l 42, 43, 53, 54; 310/15 Rich ..290/53 X 1451Oct. 3, 1972 3,553,726 1/1971 Zimmerman ..3|0/1s PrimaryExaminer-Bernard A. Gilheany Assistant Examiner-W. E. Duncanson, Jr.Attorney-Wenderoth, Lind & Ponack ABSTRACT 7 Claims, 8 Drawing FiguresJAMES DAVID LAST and DAVID NORMAN ETHEREDGE RUNS,

Inventors 'HLMIZLMJIM Attorneys PATENTED E 3 I972 SHEET U BF 4 JAMESDAVID LAST and DAVID NORMAN ETHEREDGE ROWE Inventcrs Attorneys METHOD OFGENERATING ELECTRICITY AND ELECTRICAL GENERATOR The invention relates toa generator for generating electricity from oscillatory motion such asthat of sea waves, vehicle suspensions, pedestrians or animals.

According to one aspect of the invention there is provided an electricgenerator comprising a stator an armature movable relative to thestator, spring means coupling the armature to the stator, thearrangement being such that bodily acceleration of the generator causesrelative movement of the armature and stator; and means for extractingelectrical power resulting from the relative movement. It is to beunderstood that the stator may provide a magnetic field and the armaturecomprise a coil system movable in the field from which the outputcurrent is drawn. Alternatively, the armature may provide the magneticfield and the stator may carry the coil system. Conveniently themagnetic field is provided by permanent magnets.

The generator may be mounted on a floating buoy or boat, on a wheeledvehicle, or on a pedestrian or a horse, for example, in which case thesaid natural frequency is the frequency of vertical jogging arising atthe desired walking pace. Except, perhaps when the mounts is aparticular kind of vehicle the frequency of the bobbing or jerkingmotion which gives the accelerations necessary to generate electricitywill usually have periodic times of at least /4 second, more usually ofthe order of l or 2 seconds and sometimes, for large boats, for example,of many seconds perhaps of the order of IO seconds or more. The naturalperiod of oscillation of the armature and stator under the influence ofthe spring means is preferably between 0.25 seconds and ten seconds.This may be adjustable.

Preferably the generator has a frame to which the armature or the statoris fixed and a mass fixed to the stator or armature movable with respectto the frame.

Preferably the mass oscillates linearly and is mounted on a linearspringconveniently a metal coil spring or a rubber spring. With thisarrangement it is convenient for the stator and armature arrangement tobe linear and for the mass to be fixed directly to the armature. In oneembodiment of the invention the mass is a permanent magnet whichconstitutes the armature.

One embodiment of the invention provides a buoy including a lineargenerator as above described mounted vertically therein, thehydrodynamic characteristics of the buoy giving it a particular naturalfrequency of bobbing in the water and the natural frequency of the masson its suspension with the buoy being arranged to be at or near thenatural frequency of the buoy.

Generators in accordance with the invention may be used for rechargingaccumulators which power light electrical equipment such as radioreceivers or transmitters, scientific instruments, recorders and thelike. A buoy-mounted generator may be used to power a warning lamp orsiren or power may be conveyed ashore by cable. However, particularapplication is found in oceanographic buoys, either anchored orfreefloating, which collect data for recording or transmission. Agenerator of the kind described above is suitable for powering theinstruments of such a buoy over long periods of time.

The invention will further be described with reference to theaccompanying drawings, of which:

FIG. I is a cross-sectional elevation of a generator according to theinvention;

FIG. 2 is a cross-sectional elevation of another generator according tothe invention;

FIG. 3 is a cross-sectional elevation of another generator according tothe invention;

FIG. 4 is a cross-sectional elevation of another generator according tothe invention;

FIG. 5 is a front elevation of a form of buoy suitable for including agenerator such as is shown in FIGS. 1 to 3; and

FIGS. 6, 7 and 8 are diagrams illustrating further embodiments of theinvention.

Referring to FIG. 1 the generator comprises a frame 1 constituted byfour rods 2 bolted at their ends to a plate 3 and a stator 4. Stator 4is formed of permanently magnetized annular laminations of a magneticceramic material. Six salient poles of alternate polarity are provided.Magnetic flux paths are indicated schematically on the drawing. An axialmagnetic core 5 is bolted at its ends to the plate 3 and the stator anddefines with the stator an annular gap 6.

An armature 7 is wound on a cylindrical part 8 of an armature carrier 9,the armature having a two-phase distributed winding with regard to thepole spacing. The carrier 9 is suspended from the plate 3 by steeltension springs 10 and a lead mass 11 is fixed to the carrier. Outputleads (not shown) are taken from the armature coils along the carrierand connected to the springs. Output current is derived from theterminals 13 connected to the upper ends of the springs. The outputcurrent is rectified and used to charge storage batteries (not shown).

Vertical accelerations of the generator as a whole give rise to linearoscillations of the armature as a result largely of the inertia of mass11. The resulting oscillating current is rectified and used. It isbeneficial to arrange that the natural period of oscillation (if any) ofthe driving means on which the generator is mounted is matched to thenatural period of oscillation of the armature. However, the oscillatorymovement of the armature is heavily damped, largely because of theextraction of electrical power. This means that in practice there is afairly wide matching tolerance and although it is not envisaged that thegenerator will be used with driving means having a natural period ofmore than IO seconds or so (e.g. a sea swell) it may be possible toderive satisfactory results from a generator the natural frequency ofwhich is up to 10 seconds. The natural period of the generator may beadjusted if desired by adjustment of the mass 11 or by changing thesprings, for example.

Damping is minimized by nylon collar bearings or ball or roller bearings(not shown) by which the armature carrier is mounted on the core.

Typical operational data for one prototype example of a generatorconstructed in accordance with FIG. I are as follows:

Approximate weight of prototype asembiy lOOKg.

Height of prototype assembly 2M.

Ratio of mass to spring rate l:l5.5 Resonance of suspended system l.5sec. period (approx) Ratio of flux density to turns in electrical system0.5mW/,,2lturn (derived from 1,000 T/phase and Magnetic ceramic materialMagnadur ll Power output (of the order of) 7.5 Watts Referring now toFIG. 2 there is shown a generator similar to that of FIG. 1. Theprincipal difference is that a cylindrical casing is provided instead ofthe rods 2 of FIG. 1. This gives a more compact and stronger assembly.in addition, casing 15 is hermetically sealed at its ends to plate 3 andthe stator. The interior of the casing is filled with nitrogen whichaffords corrosion protection. Another difference over the FIG. 1arrangement is that rectifiers and charging control circuitry 16 arecarried by the armature carrier, the armature winding being connected tothe rectifiers which give a direct current output through the springs tocharge the batteries (not shown).

Referring now to FIG. 3 there is shown a modification of the generatorin which the armature carrier is mounted on compression springs 17 woundon the rods 2 of the frame. This gives a construction which is shorterand wider than the arrangements described with reference to FIGS. 1 and2. Also, the platform 18 of the armature carrier supports the batteries19 as well as rectifiers and charging control circuitry 16. This meansthat mass 1 1 can be reduced considerably.

F l6. 4 shows an alternative arrangement for the generator in which thestator is constituted by the twophase coil 23 wound on the core 5. Thearmature is constituted by a permanent magnet assembly 24 which issimilar to the stator assemblies of FIGS. 1 to 3 but which is mounted ina mild steel yoke 24a and arranged to be movable longitudinally, itbeing suspended for oscillation by elastic thongs 25.

F IG. 5 shows schematically an oceanographic research buoy which carriesa generator as described with reference (for example) to FIG. 1. Thebuoy has a body 20 in which the generator 21 and storage batteries 22are housed. The buoy carries research instruments which are powered bythe batteries and a radio transmitter also powered by the batterieswhereby information from the instruments is transmitted. It is foundthat for optimum results in given seas a good natural period ofoscillation for the armature is 1.5 seconds.

Referring now to FIG. 6 there is shown a generator in accordance withthe invention which is particularly suitable for deriving electricityfrom rolling motion. The generator comprises a platform 26 of magneticmaterial in which is wound a distributed two-phase winding (not shown).A cylindrical armature 27 is allowed to roll from side to side acrossthe platform under restraint from springs 28. The armature comprises amagnet with six poles of alternate polarity and as the armature rollsbecause of the effects of inertia, flux from the magnets cuts the statorcoils and generates current therein.

FIG. 7 shows an embodiment of the generator constituted by a permanentmagnet 29 which is the bob of a pendulum pivoted at 30 and restrained bysprings 31. The stator is constituted by a two-phase winding on anarcuate magnetic former 32.

FIG. 8 shows another pendulum arrangement, in which the pendulum iscompound, having a mass 33 on one side of the pivot 34 and a magnet 35on the other side of the pivot. A single tension spring 36 serves tourge the magnet to a central position with respect to a distributed coilsystem 37 constituting the stator.

It is to be understood that the invention is not restricted to thedetails of the foregoing description made with reference to the drawinFor exam le, it is clear that the roles of the armaturg and stator enaybe reversed the stator may be wound and/or may be movable wheres thearmature may be constituted by a permanent magnet and/or may be fixed.instead of current being extracted by means of the springs, flexibleleads may be used. A coaxial rotary system in which the springconstraint is applied and coil moves relative to field may also beemployed (e.g., for rolling applications). It is envisaged that size mayvary from approximately 0.5m volume (giving perhaps up to 50W power) to0.01m (giving perhaps 0.5W power), the example given with reference to FIG. 1 having a volume of 0.2m and giving 7.5W power. Generators may besingle phase, two-phase, or multiple phase as best to use the availablewinding volume. Clearly, a linear arrangement such as that shown in FIG.1 may be operated horizontally in some applications instead ofvertically as shown.

We claim:

1. An electric generator comprising a stator with a longitudinal axis,the stator having a magnetic core extending along said axis; amulti-polar permanent magnet assembly fixed with respect to the core andspaced apart therefrom to define therewith a longitudinal gap parallelto the axis and establishing a magnetic field across the gap; anarmature winding situated in the gap, the armature winding beingcomposed of a plurality of distributed phase windings and being movablelongitudinally in the gap; spring means coupling the armature winding tothe stator, the arrangement being such that bodily acceleration of thegenerator causes movement of the armature winding in the gap; and meansfor extracting electrical power from the armature resulting from saidmovement.

2. An electric generator as claimed in claim I wherein the naturalperiod of oscillation of the armature winding and permanent magnetassembly is between 0.25 and 20 seconds.

3. An electric generator as claimed in claim 1 wherein the armaturewinding is carried on a carrier, the output therefrom is rectified byrectifiers carried on the armature carrier and the rectified output isused to charge storage batteries.

4. An electric generator as claimed in claim 3 wherein the storagebatteries are also carried on the armature carrier.

5. An electric generator as claimed in claim 1 carried in a buoy adaptedto float in the sea.

6. An electric generator as claimed in claim 5 wherein the naturalperiod of oscillation of the armature winding and permanent magnetassembly is approximately 1.5 seconds.

7. An electric generator as claimed in claim 1 included in a sealedhousing which is evacuated or filled with nitrogen.

l i i

1. An electric generator comprising a stator with a longitudinal axis,the stator having a magnetic core extending along said axis; amulti-polar permanent magnet assembly fixed with respect to the core andspaced apart therefrom to define therewith a longitudinal gap parallelto the axis and establishing a magnetic field across the gap; anarmature winding situated in the gap, the armature winding beingcomposed of a plurality of distributed phase windings and being movablelongitudinally in the gap; spring means coupling the armature winding tothe stator, the arrangement being such that bodily acceleration of thegenerator causes movement of the armature winding in the gap; and meansfor extracting electrical power from the armature resulting from saidmovement.
 2. An electric generator as claimed in claim 1 wherein thenatural period of oscillation of the armature winding and permanentmagnet assembly is between 0.25 and 20 seconds.
 3. An electric generatoras claimed in claim 1 wherein the armature winding is carried on acarrier, the output therefrom is rectified by rectifiers carried on thearmature carrier and the rectified output is used to charge storagebatteries.
 4. An electric generator as claimed in claim 3 wherein thestorage batteries are also carried on the armature carrier.
 5. Anelectric generator as claimed in claim 1 carried in a buoy adapted tofloat in the sea.
 6. An electric generator as claimed in claim 5 whereinthe natural period of oscillation of the armature winding and permanentmagnet assembly is approximately 1.5 seconds.
 7. An electric generatoras claimed in claim 1 included in a sealed housing which is evacuated orfilled with nitrogen.